Author
Topic: Repeat-o-meter (Read 3050 times)

Here is a video about a Repeat-o-meter that I have just built. it is for checking surface plates for hollows in the surface. This build is directly related to the 91cm x 91cmx 15cm granite surface plate that I just bought in preparation for scraping and the Richard King Scraping class in December! I have also been following a Tom Lipton John sanders collective build of the same tool. i realise that I didn't give an explanation about why I used the lathe to grind the feet flat, I don't have a big belt sander or a surface grinder, so it was the only way to get all four "feet" flat!

One thing I missed seeing in the video is the Repeat-O-Meter in use on the surface plate you wanted to check with it at the start. How is it used, and was the plate flat?

Also..... sorry I'm not familiar with this tool..... if the balls are pressed in, how does the gauge end move up and down? Wasn't there a ball under that one? And if the two stabilizer bars on the side are loose, what do they do -- or do you tighten them up?

I'm sure there are answers to all this, once you own one. But your video is the only thing I know about it!

One thing I missed seeing in the video is the Repeat-O-Meter in use on the surface plate you wanted to check with it at the start. How is it used, and was the plate flat?

i hadn't tried it when I filmed it, i thought I'do a video of mapping out the plate to follow!

Also..... sorry I'm not familiar with this tool..... if the balls are pressed in, how does the gauge end move up and down? Wasn't there a ball under that one? And if the two stabilizer bars on the side are loose, what do they do -- or do you tighten them up?The steel balls are pressed in and then ground flat, I finished them with wet 'n dry abrasive paper, once the balls were nice and smooth, I made a flexion by drilling a hole close to the bottom edge and slitting from the top down into the hole, leaving 1.2mm+/- so that the single ball/foot under the dial gauge can move up and down (within the elastic limit of the flexion!) whilst the three that remain under the mass of the body sit on a flat area of the surface plate. Them two "floppy" bars on the side are there to stop the lower front bar from "drooping" as there's nothing there to support it but the flexion. I think that these are more of a safety feature than anything else! I included a link to a Tom Lipton video that explains the us of the Repeat-o-meter

I'm sure there are answers to all this, once you own one. But your video is the only thing I know about it!

So the ball under the gauge is not pressed into place like the others, but is free to move up and down? And the side bars effectively put a limit on the upper and lower range of movement of the indicator -- hope I have that right?

So the ball under the gauge is not pressed into place like the others, but is free to move up and down? And the side bars effectively put a limit on the upper and lower range of movement of the indicator -- hope I have that right.

Nope! All four balls are pressed in, there is a flexion that is situated next to the two central balls, this allows the 20 x 50mm bar to bend near the middle, three of the balls under the heavy end provide a reference point, the remaining ball is under the dial gauge indicator. The side bars are there to stop the flexion bending too much and going beyond it's elastic limit!

Nope, the upper part is (semi) rigid beam, that screw disc is only for adjustment.

The lower body is split half - there is a flexure (hole cut free from other side). All balls are rigidly attached. Three balls support the back of the meter and this "beam" on the top. Front part is sort of tailgate, this flexure allows it to follow countour of the surface plate.

Those loosely attached arms on the side work exactly the same way that tail gate keepers on pick-up truck. Prevent that part from dropping down when the instrument is lifted.

Purpose of the balls is to give a defined contact, when flat is not flat enough - you can describe a plane with three points, then you fourth somewhere and indicate how much it it is different.

I'm glad it's useful! the "flexion" is 1.35mm. unlike the Rahn version, I drilled and reamed a hole for the flexion. I built mine without known dimensions, so I finished up with one that is a little on the long side which means that it is a little more sensitive! the standard Imperial one is 5" from middle feet to measuring foot but there is a metric version which is 100mm. I used cold rolled for the base plate (I had it!), but hot rolled would be fine.

I was eyeballing and estimating the Rahn version, but based on my past experience I very much prefer drilled/reamed hole to terminate such a cut.

I'm drawing parts based on 100+100 spacing. Bit torn between ballbearing balls pressed on tight holes (I have a fitting drill) or going trough unused circular inserts for lathe/mill. I have proper screws, drills/taps. Might be easier that way.

I have very nice Mitutoyo 2109S-10 0,001 mm resolution indicator, but reading is a bit tight and i doubt that this would benefit that much linearity....very tempted to use cheap 0,001 mm resolution dial on this one.

Hope that this flu does not get worse. This might be just the right weekend project.

HRS is 20*50 mm and then I have some 5*50 mm for spacers. Can't find any 10(or 12) mm *50 mm for DTI arm and other parts, should hit junkyard, but it is closing early today.

Pekka1.35mm seemed on the thick side to me, but it worked well. I think it's important to remember it's in the flexible range of the metal. The two limiting bars on the side are intended to keep the flexion in the limits of flexibility, mine are a bit slack, but it isn't a worrying amount of movement. The actual movement that I've found on my surface-plate is less than 0.01mm, so you can really limit the movement!